If you drop the pan again install a drain plug. Makes future work much less messy.
Heavy machinery ATF? Mistake. Castrol Dex/Merc. Whining is pump cavitation, and you are sucking a milkshake through a straw and it is expecting Coca Cola viscosity.
Didn’t pull tube? Mistake, you have to put new orings on case side.
There is too much TH400 advice geared towards the drag strip out there, even in Kirby’s book. Shift kits, valve body adaptions, etc. Don’t do any of it.